You'll need to get a custom tune, but everything else would be fine for what you're doing. As far as a cam goes, you're not going to want anything bigger than a 212/218. The Brian Tooley Racing stage 1 truck cam kit is 206/212 and would likely suit you best, but I recommend contacting the vendor to get their thoughts. Would also ask Cam Motion about their truck cams. With any cam, you're going to need to replace the valve springs.
How much of an overhaul are you talking about? Personally, I wouldn't worry about rod bearings or anything of that nature unless there's an issue in the bottom end. For my 5.3 I mainly just did some cleaning, slammed the cam in, jammed in new lifters, and slapped new gaskets on.
The tow/haul mode only has an affect on the behavior of the transmission and not the performance of the engine. In tow/haul mode can change things like shift points and how the truck holds a gear. For example, in Basic Birch, if I hit the tow/haul switch at 30 MPH, my trans will drop to 1st and hold it there but won't do any bucking if I let off the gas. At 60-70 MPH, it'll do the same thing except it drops down to 2nd gear. This is great for WOT pulls since the trans won't be taking time to downshift and it's not as hard on the transmission (presuming adequate cooling).